The present invention relates to an optical pickup device for reading information recorded on an optical recording medium and/or writing a signal on an optical recording medium, a semiconductor laser device and a housing usable for the optical pickup device and a method of manufacturing such a semiconductor laser device.
Semiconductor laser devices are widely used as components of optical pickup devices in order to read the information recorded on information recording media such as CD-ROM (Compact Disc Read-Only Memory), MD (Mini Disc) and so on. The semiconductor laser devices include a frame type semiconductor laser device as disclosed in JP 2002-43679 A. The frame type semiconductor laser device has a package in which a metal lead frame and a plurality of leads that serve as electrodes are integrated with a resin (outer casing). A semiconductor laser chip (“laser chip”) is mounted in an element-placing portion (a portion on which a chip is to be mounted) of the lead frame, and the laser chip and the electrode leads are electrically connected to each other via wires. JP 2002-43679 A is intended to improve the heat dissipation efficiency by providing the lead frame with wing portions projecting from side surfaces of the resin.
However, recent optical pickup devices often employ high-power laser chips, and it is necessary to further improve the heat dissipation characteristics of the laser chips.
JP 2002-43679 A also discloses an example in which the laser chip is mounted in the element-mounting portion via a submount. In this example, the submount is constructed of a Si substrate with a built-in monitoring photodetector, and the laser chip is mounted on the substrate with solder or the like. In operation, the laser chip emits laser light forward and also backward. The laser light emitted backward is partially incident on the monitoring photodetector, and the laser light to be emitted forward from the laser chip is controlled on the basis of the output of the monitoring photodetector.
However, in this example, the greater part of the laser light emitted backward from the laser chip is not incident on the monitoring photodetector due to restrictions on the arrangement of the laser chip and the submount. Therefore, the quantity of light incident on the monitoring photodetector may be so little that it may cause inconvenience in controlling the laser light to be emitted forward from the laser chip.
In a frame type semiconductor laser device described in JP 2003-31885 A, an outer casing, which surrounds the peripheries of a laser chip and a monitoring photodetector, is provided, and a light-reflecting surface is provided on a part of the inner surface of the outer casing. The laser light emitted backward from the laser chip is reflected on the light-reflecting surface, and the greater part of the light is incident on the monitoring photodetector.
However, in the example of JP 2003-31885 A, if a stress is applied to the outer casing while the semiconductor laser device is being mounted on an electronic device such as an optical pickup device, the light-reflecting surface may be distorted. As a result, disadvantageously, the quantity of light incident on the monitoring photodetector may not be stabilized.
JP 2003-31885 A also discloses that the outer casing is constructed of two parts of a lower part and an upper part, and the upper outer casing is attached as a cover (cap) for protecting the laser chip to the lower outer casing by press fitting or the like.
When attaching the upper outer casing to the lower outer casing by press fitting, the upper outer casing is brought in pressure contact with the lower outer casing by being urged in a direction roughly perpendicular to the optical axis of the laser chip. Therefore, when transmitted to the lead frame, the stress applied to the lower outer casing is transmitted in the direction roughly perpendicular to the optical axis of the laser chip. A window portion is formed at the lower outer casing so as not to interrupt the laser light from the laser chip.
As is apparent from above, since the stress is applied to a portion including the window portion (which portion is of a small strength) of the lower outer casing, it is possible that the stress cannot be sufficiently absorbed by the lower outer casing and transmitted to the lead frame, disadvantageously causing the warp or bending of the lead frame.